1. Field of the Invention
The present invention relates to an air bag cover comprising a TPE layer, or a surface sheet with a TPE layer provided.
Although an embodiment of an air bag cover for an air bag device to be assembled in an instrument panel is explained herein, the invention is not limited thereto, but it can be adopted in an air bag cover for an air bag device to be assembled in a side door, a pillar, a front or back sheet, or the like.
Hereafter, abbreviations for polymers mainly used in this specification are presented.
PE . . . polyethylene
PP . . . polypropylene
PS . . . polystyrene
PVC . . . polyvinyl chloride
BR . . . butadiene rubber
EPDM . . . ethylene propylene non-conjugated diene three element copolymer rubber
EPM . . . ethylene propylene copolymer rubber
IIR . . . butyl rubber
SBR . . . styrene butadiene rubber
TPE . . . thermoplastic elastomer
Moreover, the breaking elongation of the surface sheet (cutting elongation: EB) and the breaking strength (tensile strength: TB) in this specification are based on a specific tensile test in the test examples described later.
2. Description of the Related Art
As an air bag cover configuration in an air bag device assembly portion (the portion of the line IIxe2x80x94II in FIG. 1) in an instrument panel 12 shown in FIG. 1, for example, those shown in FIG. 2 have been provided. As a known published product with the similar configuration, Unexamined Japanese Patent Publication No. 11-222089, or the like can be presented.
That is, the configuration comprises a cover surface sheet part 14a and a cover base body 16, with a base body door part 16a of the cover base body 16 provided with a hinge groove 18 and a tear line groove 20 on the back side. The cover base body 16 is produced as a first injection molding product, provided integrally with an instrument panel base body 22 as a second injection molding product, on the inner side thereof by two-part injection molding.
Here, the cover surface sheet part 14a is formed as a part of an instrument panel surface sheet 14. The configuration of the surface sheet 14 can be, for example, a three layer configuration from the back side, of a barrier layer 24 made of a thermally resistant resin material, a foamed layer 26 made of a soft foamed resin material, and a decorative layer 28 made of a soft synthetic resin (in general, it is a thermoplastic elastomer xe2x80x9cTPExe2x80x9d) as shown in the figure.
The air bag cover of the configuration is produced, in general, by shaping the three layer configuration sheet by vacuum molding, and two-part injection molding in the order of the cover base body 16 and the instrument panel base body 22. At the time of the vacuum molding of the sheet, a relief line groove 30 is formed in the vicinity of the hinge groove 18 and the tear line groove 20 near the cover surface sheet part 14a by mold shaping. The relief line groove 30 is mainly for smoothly performing the hinge function and the tear line function. The tear line groove 20 is formed by, for example, providing a notch by an ultrasonic cutting, or the like.
At the time the air bag 34 is expanded, stress is concentrated on the tear line groove 20 formation portion (thick part) of the cover base body 16 so as to rupture the tear line groove 20 formation portion. In the foamed layer 26, stress is concentrated on the portion of the cover base body 26 with the shortest distance with respect to the tear line groove 20 bottom part (minimum section portion) so as to form a crack toward the relief line groove 30 tip end portion. The relief line groove 30 is ruptured by stress concentration on the tip end portion of an embedded pleat part 28a of the surface sheet 14.
An air bag cover 11 is jointed to the air bag device 10 via front and rear mounting walls 31, 32, projecting from the back surface of the cover base body 16. The rear mounting wall 32, which is formed straight at the time of molding, has a tip end mounting part 32a bendable like a hinge at the time of mounting (see FIG. 5).
The air bag device 10 comprises basically an air bag 34, an inflator 36, a bag case 38 for storing and attaching the same with the air bag cover 11, and a diffuser pipe 40. In the example shown in the figure, the bag case 38 having a planar lateral rectangular box-like shape, comprises engaging claws 42, 42 on both sides in the longitudinal direction each by a predetermined distance, and therebelow front and rear receiving bars 48, 48 comprising front and rear receiving grooves 44, 44 to be fitted with the lower ends of front and rear mounting walls 31, 32. Moreover, the diffuser pipe 40 having a configuration wherein upper and lower half-split member 40a, 40b are jointed on both sides by a flange, is integrated with a bottom part inside flange 38a of the bag case 38 by a bolt 52, or the like by co-fastening. At the time, by co-fastening the opening part of the folded air bag 34 simultaneously via a retainer ring 35, the air bag 34 is attached and stored in the bag case 38. By pushing the front and rear mounting walls 31, 32 into the receiving grooves 44, 44, the engaging claws 42, 42 are fitted and engaged with engaging holes 50, 50 formed in the front and rear mounting walls 31, 32 so as to joint the air bag device 10 and the air bag cover 11.
In the case of the air bag cover of the above-mentioned configuration, in order to support the rotation opening at the time of expanding the bag of the bag door part, existence of the relief line formed by embedding the surface sheet decorative layer, is essential. Due to the existence of the relief line, the air bag cover is limited in terms of design as well as a complicated vacuum molding mold of the surface sheet is needed as mentioned in the above-mentioned official gazette. Particularly in the case a sophisticated breaking rapidity is required in the tear line, the relief line is need to be formed relatively deeply so that a thin and high rib for a relief line needs to be formed in the vacuum molding mold. The rib formation further increases the difficulty in the mold production as well as deteriorates the mold durability.
In view of the circumstances, an object of the invention is to provide an air bag cover capable of relatively reducing the depth of or eliminating a relief line groove formed by the embedded pleat part of the surface sheet (decorative layer).
In order to solve the problems, the inventors have found out that the door opening performance can be ensured at the time of expanding the bag with a shallower depth of or without formation of the relief line groove by reducing the stretchability of the surface sheet in the effort in the elaborate development process so as to invent the air bag cover with the following configuration.
An air bag cover comprising a TPE layer, or a surface sheet with a TPE layer provided on the surface side, wherein the breaking elongation of the TPE material for the TPE layer is adjusted by containing a filler, is provided.
According to the configuration, stress is concentrated from the back side on the tear line groove formation portion, which is a notch portion, in the bag cover at the time of developing and inflating the air bag. At the time, since the breaking elongation is set at a lower level by containing an inorganic filler in the TPE material, it is broken rapidly at the tear line groove compared with the conventional examples. Therefore, the relief line groove can be provided shallower with respect to the tear line groove of the bag cover compared with the conventional examples, or can be eliminated.
As the embodiments of the air bag cover capable of adopting the invention, the following air bag covers can be presented.
An air bag cover having a surface sheet with a plural layer configuration comprising from the back side a barrier layer made of a thermally resistant resin material, and a decorative layer made of a TPE material, with or without a foamed layer made of a soft foamed resin material provided there between, with the surface sheet provided integrally with a cover base body.
An air bag cover having a surface sheet with a two layer configuration comprising from the back side a foamed layer made of a soft foamed resin material, and a decorative layer made of a thermoplastic elastomer (TPE) material, with the surface sheet provided integrally with a cover base body.
An air bag cover having a surface sheet with a one layer configuration comprising only a decorative layer, surface sheet and a cover base body provided integrally via a foamed layer provided by injecting resin between the cover base body and the surface sheet.
The content ratio of a filler in the case the filler is an inorganic filler, is in general, about 5 to 30% by mass, preferably about 5 to 13% by mass. The range of the content ratio of the filer facilitates the breaking rapidity of the surface sheet so as to achieve the object of the invention.
Moreover, the breaking elongation (in a specific tensile test) of the TPE material in the case a filler is contained in the TPE material is about 100% or less, preferably about 50% or less. Thereby, the breaking rapidity of the surface sheet can further be facilitated so as to achieve the object of the invention.